JP-B-4-60302(the term "JP-B" as used herein means an "examined published Japanese patent application") discloses a technique for preventing an increase of impedance in the inside of batteries during storage by adding a borate, a silicate, etc. of an alkali metal or an alkaline earth metal to a mixture of the positive electrode active material comprising manganese dioxide.
In order to improve safety in case of an overcharge, it has been suggested to add lithium oxalate to LiCoO.sub.2 (JP-A-4-329269, the term "JP-A" as used herein means an "unexamined published Japanese patent application") or to add lithium carbonate to LiCoO.sub.2 (JP-A-4-329268 and JP-A-4-328278). However, these techniques cannot reduce the occurrence of rupture in case of rapid temperature rise or heating.
Nonaqueous batteries using a lithium-containing transition metal oxide, such as LiCoO.sub.2, LiNiO.sub.2 or LiMn.sub.2 O.sub.4, as a positive electrode active material and a substance capable of intercalating and deintercalating a lithium ion (e.g., an Li-containing metal oxide or calcined carbonaceous material) as a negative electrode active material have a higher cut-off voltage in charging than conventional alkali batteries, usually of from 3.5 to 5 V, and have been attracting attention as high-energy density and high-safety batteries. A wide variety of the nonaqueous batteries have been put to practical use (JP-A-55-136131 and JP-B-3-30146).